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A cord is used to lower vertically a block of mass M a distance d at a constant downward acceleration of g/4. (a) Find the work done by the cord on the block. (b) Find the work done by the force of gravity.

A cord is used to lower vertically a block of mass M a distance d at a constant downward acceleration of g/4. (a) Find the work done by the cord on the block. (b) Find the work done by the force of gravity.

Grade:upto college level

3 Answers

Navjyot Kalra
askIITians Faculty 654 Points
8 years ago
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Amiyanshu
13 Points
6 years ago
Check the net force on the object and then write the equation of motion.Tension and gravity are working on the object and motion is in direction of gravity. Hence the equation of motion is,Mg-T= ma. -(1)As the acceleration of the object is given as he as the acceleration of the object is given as G divided g divided by 4.T=3mg/4(A) work done =force×displacementAs we know that displacement is in opposite direction of force.Hence workdone is (-ve).W=-f.dW=-(3/4)×Mg×d(B) now work done by gravity is in direction of displacement hence it is positive.W=force(of gravity)×displacement W=Mgd
Kushagra Madhukar
askIITians Faculty 628 Points
3 years ago
Dear student,
Please find the solution to your problem.
 
We have,
T – Mg = Ma
T = Mg + M( – g/4)
   = ¾ Mg
Hence, work done by tension, WT = T.(–d) = – Td
                                                  = – ¾ Mgd
 
The work done by Gravity, Wg = Fg.(d)
                                            = Mgd
 
Thanks and regards,
Kushagra

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